[docs] Indices stats groups in nodes api

Closes #5349
Add cluster_name to cluster_state

Today the clusterstate is not asssociated with the cluster_name which is odd
since it's pretty much it's only valid identifier. Any node can send a cluster
state to another node today even if it's not the same cluster. These situations
can happen rarely during tests or even in the wild by accident.
Discard new cluster state if the clustername doesn't match

Closes #5622
InternalEngine - back to set dirty=false just *before* a refresh is done

reverting: 5553c383bca1f8b5437aa0eb34e291824e9057fb
Mock Transport: Allow to simulate network failures
An infrastructure that allows to simulate different network topologies failures, including 2 basic ones in failure to send requests, and unresponsive nodes
closes #5631
Added trace logging in TransportSearchTypeAction and a delayed verification of test failures in MinDocCountTests.testMinDocCountOnTerms